Program and Abstract Book - SRON
Program and Abstract Book - SRON
Program and Abstract Book - SRON
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19 th International Symposium on Space Terahertz Technology<br />
P2-5<br />
Integration of IF Amplifiers with NbTiN SHEB Mixers<br />
P. Pütz 1 , C.E. Honingh 1 , M. Justen 1 , K. Jacobs 1<br />
J. Bardin 2 , H. Mani 2 , S. Weinreb 2<br />
1 KOSMA, 1. Physikalisches Institut der Universität zu Köln, Germany<br />
2 Department of Electrical Engineering, California Institute of Technology, Pasadena CA 91125<br />
For the 1.4 THz <strong>and</strong> 1.9 THz channels of the GREAT instrument for SOFIA we have<br />
developed waveguide mixers with NbTiN superconducting Hot Electron Bolometer (SHEB)<br />
devices on low stress silicon nitride membranes. Comparable mixers will also be used in the<br />
balloon-borne Stratospheric Terahertz Observatory (STO). In the current baseline approach<br />
for these receivers, the mixer is connected to the low noise IF amplifier by a narrow-b<strong>and</strong><br />
(1.2–1.8 GHz) cryogenic isolator to prevent interactions between the 1–2 GHz amplifier <strong>and</strong><br />
the mixer. Previous tests have indicated that an isolator is necessary for a stable receiver<br />
performance with minimal variations of noise <strong>and</strong> gain vs. IF frequency. Unfortunately, the<br />
isolator has the disadvantage that a significant fraction of the potential IF b<strong>and</strong>width of the<br />
mixer <strong>and</strong> low noise IF amplifier is wasted.<br />
Several approaches are currently being pursued for wide-b<strong>and</strong>width integration of mixers <strong>and</strong><br />
IF amplifiers <strong>and</strong> experimental results will be reported at the conference. A first approach is<br />
a connection of a Caltech 0.5–11 GHz indium-phosphide LNA directly to the mixer without<br />
an isolator; initial results have shown large frequency ripple in the measured receiver noise<br />
temperature. The amplifier has excellent noise <strong>and</strong> flat gain when driven from a 50 ohm<br />
generator but does not present a 50 ohm load to the HEB mixer at IF frequencies below 4<br />
GHz. The use of a small attenuator between LNA <strong>and</strong> mixer will be investigated. Finally, a<br />
new silicon-germanium (SiGe) LNA for the 0.3 to 5 GHz range with good input match is<br />
under test at Caltech <strong>and</strong> further tests of integration with the HEB mixer are planned prior to<br />
the conference.<br />
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